The present invention relates generally to magnetic resonance (MR) imaging systems and, more particularly, to an RF receiver assembly capable of translating multiple channels of MR signals across a single readout cable. The present invention is particularly applicable with multi-coil architectures.
When a substance such as human tissue is subjected to a uniform magnetic field (polarizing field B0), the individual magnetic moments of the spins in the tissue attempt to align with this polarizing field, but precess about it in random order at their characteristic Larmor frequency. If the substance, or tissue, is subjected to a magnetic field (excitation field B1 ) which is in the x-y plane and which is near the Larmor frequency, the net aligned moment, or “longitudinal magnetization”, Mz, may be rotated, or “tipped”, into the x-y plane to produce a net transverse magnetic moment Mt. A signal is emitted by the excited spins after the excitation signal B1 is terminated and this signal may be received by a receive coil(s) and processed to form an image.
When utilizing these signals to produce images, magnetic field gradients (Gx, Gy, and Gz) are employed. Typically, the region to be imaged is scanned by a sequence of measurement cycles in which these gradients vary according to the particular localization method being used. The resulting set of received NMR signals are digitized and processed to reconstruct the image using one of many well known reconstruction techniques.
An RF coil assembly having one or more receive coils is used to sample the “echo” induced by application of magnetic field gradients and excitation pulses. Each receive coil samples the echo or MR signal and transmits the signal to a receive channel or a receive channel stack. Each receive channel then translates the acquired signal to a processing system that formats the signal into a data stream that is fed to a data acquisition system (DAS) for image reconstruction. Generally, there is a desire to increase the number of receive coils that are used to sample the induced echo. Simply put, increasing the number of coils increases overall system sensitivity to the induced echo signal. However, as the number of receive coils is added to an MR system, the need for additional parallel receiving channels also increases. The number of coils that can be implemented is not limitless as physical constraints limit the number of readout cables that can be connected between the coils and the receiver hardware of the MR system. As a result, the MR system is equipped with fewer receive coils than may be desired. This can be problematic given sensitivity to a region-of-interest (ROI) is partly the result of the number of receive coils of the MR system.
Additionally, the parallel readout cables used to translate received signals from a scan subject are typically routed in relatively large bundles from the coils to the receiver channels or hardware. As each coil is connected to the receiver hardware via a unique readout cable, any increase in the number of coils also increases the number of readout cables required. Further, there are physical limitations as to the number of receivers that can be provided within a given receiver cabinet of an MR system, which further limits the potential number of cables and receivers that may be used in constructing an MR system.
It would therefore be desirable to have a system capable of routing multiple channels of MR data across a single readout cable. It would also be desirable to process acquired signals to utilize the receiver and transport channels of an MR system more efficiently.